Modification of catalytic activity of synthetic zeolites

ABSTRACT

A method is provided for effectively tailoring the catalytic activity of synthetic crystalline zeolites. The method involves synthesizing the zeolite from a reaction mixture containing a source of bulky organic cations, contacting the synthesized zeolite with hydrogen fluoride solution, calcining the hydrogen fluoride solution contacted zeolite, contacting the calcined zeolite with an ammonium exchange solution, and then calcining the ammonium exchange solution contacted zeolite.

CROSS-REFERENCE TO RELATED CASES

This application is related by subject matter to applications Ser. No.382,830 and 382,892, filed on the same date herewith.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for altering the surface catalyticactivity of synthetic crystalline zeolites (e.g. of the ZSM-5 type)which involves the sequential steps of synthesizing the crystallinezeolite from a synthesis reaction medium containing a source of bulkyorganic cations, contacting the "as synthesized", uncalcined crystallinezeolite product with hydrogen fluoride solution, calcining the hydrogenfluoride solution contacted zeolite, contacting the calcined zeolitewith an ammonium exchange solution, and then calcining the ammoniumexchange solution contacted zeolite.

2. Description of Prior Art

The use of zeolites as catalyst components is well known. Nevertheless,zeolites have been the subject of extensive investigations to improvetheir catalytic properties. Zeolites ZSM-5 and ZSM-11, for example, arefully described in U.S. Pat. Nos. 3,702,886 and 3,709,979, respectively,wherein it is disclosed that because of their ordered, porous structure,creating small interconnected cavities, they are selective towardcertain molecules and provide catalytic capabilities for variouschemical conversion reactions. U.S. Pat. Nos. 4,088,605 and 4,148,713disclose a process combination wherein zeolites of the ZSM-5 type havetheir outer shells altered so as to be essentially aluminum-free,leading to a more selective catalyst. However, no known art discloses orsuggests modifying the surface of synthetic zeolites, such as those ofZSM-5 type, by altering their surfaces and the alpha activity of thesurfaces and thereby altering their catalytic properties by the presentmethod.

It is noted that U.S. Pat. Nos. 3,354,078 and 3,644,220 relate totreating crystalline aluminosilicates with volatile metal halides.Neither of these latter patents, however, is concerned with alteringsurface activity of synthetic zeolites of ZSM-5 type having beenprepared from reaction mixtures containing bulky ions as in the presentmethod. In fact, the use of hydrogen fluoride with aluminosilicates hasbeen avoided because of resulting lattice damage. Hydrogen fluoride inhigh concentrations, e.g., 5 N or greater, readily attacks both silicaand alumina. Lower concentrations may also damage lattice structures ifcontact is maintained for too long a time. With some zeolitic materials,hydrogen fluoride treatment under controlled conditions has been used toalter pore size. U.S. Pat. Nos. 3,997,474 and 4,054,511 relate toaltering effective pore size of natural ferrierite ore with very dilutehydrogen fluoride treatment. When the same treatment of erionite wasconducted, a large loss in activity and crystallinity resulted.

SUMMARY OF THE INVENTION

The present invention relates to a novel method for altering catalyticactivity of certain synthetic crystalline zeolites, e.g., ZSM-5 andZSM-11, which comprises the sequential steps of (1) synthesizing saidcrystalline zeolite from a synthesis reaction mixture containing asource of bulky organic cations, e.g., onium compounds or compoundshaving multiple cationic centers, (2) contacting the uncalcined, assynthesized, crystalline zeolite with hydrogen fluoride solution underspecific conditions of solution concentration, time, temperature andpressure, (3) calcining the hydrogen fluoride solution contactedzeolite, (4) contacting the calcined zeolite with an ammonium exchangesolution, and (5) calcining the ammonium exchanged zeolite.

The resulting activity modified zeolite has a surface with a designedlower alpha activity than the interior of the zeolite. It also exhibitsan X-ray diffraction pattern with a series of lines of increased breadthand decreased intensity when compared with the same zeolite which hasnot been altered by the present method.

The resulting zeolite also has improved selectivity and other catalyticproperties when compared with the same zeolite which has not beenaltered by the present method. In fact, the severity of the second stepof the present method may be varied within the given limits to providespecific selectivity for specified catalytic applications. For example,if the severity of the second step is controlled so that the alphaactivity of the surface of the treated zeolite is in the range of from50 to 150, catalytic performance for hydrodewaxing of petroleumdistillates is considerably improved.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The novel method of the present invention is concerned with themanufacture of certain synthetic crystalline zeolites, especially of theZSM-5 type, e.g, ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 andZSM-48, with unusual and desired catalytic properties.

The first step of the method involves synthesizing the ZSM-5 typecrystalline zeolite from a synthesis reaction medium containing a bulkyion source. The method of this invention does not provide the desiredfinal product when the crystalline zeolite has been synthesized withnon-bulky ion sources. While not wishing to be bound by any theory ofoperation, it appears necessary that the synthesized, uncalcined zeoliteproduct of the first step must have its channels plugged with theorganic material so that only the surface of the crystalline material isaffected by the hydrogen fluoride of the second step. Therefore, thezeolite must be synthesized in the presence of the desired organiccation source to provide the necessary channel blockage and the productmust not be calcined at this time to permit the blockage to remain.

Bulky ion sources to be used in the first step synthesis of thecrystalline zeolite include trialkylamines, wherein alkyl is from 1 to20 carbon atoms, onium compounds and compounds containing multiplecationic centers. The onium compounds include those having the followingformula:

    R.sub.4 M.sup.+ X.sup.-

wherein R is alkyl of from 1 to 20 carbon atoms, heteroalkyl of from 1to 20 carbon atoms, aryl, heteroaryl, cycloalkyl of from 3 to 6 carbonatoms, cycloheteroalkyl of from 3 to 6 carbon atoms, or combinationsthereof; M is a quadricoordinate element (e.g., nitrogen, phosphorus,arsenic, antimony or bismuth) or a heteroatom (e.g., N, O, S, Se, P, As,etc.) in an alicyclic, heteroalicyclic or heteroaromatic structure; andX is an anion (e.g., fluoride, chloride, bromide, iodide, hydroxide,acetate, sulfate, carboxylate, etc.). When M is a heteroatom in analicyclic, heteroalicyclic or heteroaromatic structure, such structuremay be, as non-limiting examples, ##STR1## wherein R' is alkyl of from 1to 20 carbon atoms, heteroalkyl of from 1 to 20 carbon atoms, aryl,heteroaryl, cycloalkyl of from 3 to 6 carbon atoms or cycloheteroalkylof from 3 to 6 carbon atoms.

The compounds containing multiple cationic centers include those havingthe formula:

    [(R).sub.3 M.sup.+ (Z).sub.n M.sup.+ (R).sub.3 ](X.sup.-).sub.2

wherein R, M and X are as above defined, Z is a bridging member selectedfrom the group consisting of alkyl of from 1 to 20 carbon atoms, alkenylof from 2 to 20 carbon atoms, aryl, heteroalkyl of from 1 to 20 carbonatoms, heteroalkenyl of from 2 to 20 carbon atoms and heteroaryl, and nis a number of from 1 to about 50. Non-limiting examples of suchmultiple cationic center containing compounds include: ##STR2##

With regard to the zeolite materials, the other components of therespective synthesis reaction mixtures as well as the synthesisconditions are given in the patents covering each material to bemanufactured by the present method. These mixtures and conditions areshown in U.S. Pat. Nos. 3,702,886 and Re. 29,948 for ZSM-5, the entirecontents of each being incorporated herein by reference. For ZSM-11 themixture and conditions are shown in U.S. Pat. No. 3,709,979, the entirecontents of which is incorporated herein by reference. The mixtures andconditions for ZSM-12 synthesis are described in U.S. Pat. No.3,832,449, the entire contents of which are incorporated herein byreference. For ZSM-23, U.S. Pat. No. 4,076,842 shows the mixtures andconditions and the entire contents thereof is incorporated herein byreference. The entire contents of U.S. Pat. No. 4,016,245 and 4,046,859,describing the mixtures and conditions for synthesis of ZSM-35 andZSM-38, respectively, are also incorporated herein by reference.

ZSM-48 can be identified, in terms of moles of anhydrous oxides per 100moles of silica as follows:

    (0.05 to 5)N.sub.2 O:(0.1 to 10)M.sub.2/n O:(0 to 4)Al.sub.2 O.sub.3 :(100)SiO.sub.2

wherein M is at least one cation having a valence n, N is a mixture of aC₂ -C₁₂, and more preferably of a C₃ -C₅, alkylamine and atetramethylammonium compound and wherein the composition ischaracterized by the distinctive X-ray diffraction pattern as shownbelow:

    ______________________________________                                        Characteristic Lines of Zeolite ZSM-48                                        d (A)        Relative Intensity (I/Io)                                        ______________________________________                                        11.8 ± 0.2                                                                              S                                                                10.2 ± 0.2                                                                              W-M                                                              7.2 ± 0.15                                                                              W                                                                4.2 ± 0.08                                                                              VS                                                               3.9 ± 0.08                                                                              VS                                                               3.6 ± 0.06                                                                              W                                                                3.1 ± 0.05                                                                              W                                                                2.85 ± 0.05                                                                             W                                                                ______________________________________                                    

These values were determined by standard techniques. The radiation wasthe K-alpha doublet of copper, and a diffractometer equipped with ascintillation counter and a strip chart pen recorder was used. The peakheights, I, and the positions as a function of two times theta, wheretheta is the Bragg angle, were read from the spectrometer chart. Fromthese, the relative intensities, 100 I/I_(o), where I_(o) is theintensity of the strongest line or peak, and d (obs.), the interplanarspacing in Angstroms (A) corresponding to the recorded lines, werecalculated. In the foregoing table the relative intensities are given interms of the symbols VS=very strong, S=strong, W=weak, andW-M=weak-to-medium (depending on the cationic form). Ion exchange of thesodium ion with cations reveals substantially the same pattern with someminor shifts in interplanar spacing and variation in relative intensity.Other minor variations can occur depending on the silicon to aluminumratio of the particular sample, as well as if it has been subjected tothermal treatment.

ZSM-48 can be prepared from a reaction mixture containing a source ofsilica, tetramethylammonium compound, C₂ -C₁₂ alkylamine, an alkalimetal oxide, e.g. sodium, with or without a source of alumina, andwater, and having a composition, in terms of mole ratios of oxides,falling within the following ranges:

    ______________________________________                                        REACTANTS      BROAD       PREFERRED                                          ______________________________________                                        Al.sub.2 O.sub.3 /SiO.sub.2                                                                  0 to 0.08   0 to 0.02                                          Na.sub.2 O/SiO.sub.2                                                                         0.01 to 1.0 0.1 to 0.5                                         N.sub.2 O/SiO.sub.2                                                                          0.005 to 0.5                                                                              0.005 to 0.25                                      OH.sup.- /SiO.sub.2                                                                          0.01 to 0.5 0.05 to 0.2                                        H.sub.2 O/SiO.sub.2                                                                          10 to 200   20 to 100                                          ______________________________________                                    

wherein N is a mixture of a C₂ -C₁₂ alkylamine and tetramethylammoniumcompound, and maintaining the mixture of 80°-200° C. until crystals ofZSM-48 are formed.

The molar ratio of C₂ -C₁₂ alkylamine to tetramethylammonium compound isnot usually narrowly critical and can range from 1:1 to 10:1. Thetetramethylammonium compound can include the hydroxide or halide withthe chloride being particularly preferred.

The second step of the present method involves contacting the assynthesized, i.e. prior to any thermal treatment, crystalline zeoliteproduct from the first step with an aqueous hydrogen fluoride solutionof from about 0.005 to about 0.5 Normal at a temperature of from aboutambient room temperature, e.g. 24° C., to about 100° C. and a pressureof from about atmospheric to about 40 psig for a contact time of fromabout 1 hour to about 10 hours. In terms of grams of zeolite/grams ofhydrogen fluoride for the second step contacting, a range of from about1/0.01 to about 1/2 must be maintained within the further conditions oftemperature, pressure and time above given. The conditions of this stepof the present method are critical and accurate control thereof withinthe above ranges is useful for tailoring the final activity of thezeolite for specific applications. For example, if the zeolite alteredhereby is intended for use in a catalyst for hydrodewaxing a petroleumfraction, such as, for example, a distillate, the activity thereof,measured by Alpha Value, should be within the range of from about 50 toabout 150, with about 100 being essentially optimum. If the catalystcomprising the altered zeolite is to be used to convert ethylbenzene,the Alpha Value of the zeolite should be within the range of from about30 to about 50, with an Alpha Value of about 40 being essentiallyoptimum. The conditions of this second step of the present methoddetermines the degree of Alpha Value modification.

The tailored structural activity by way of the second step actuallychanges the zeolite structure in a way which provides altered catalyticactivity and improved stability of the final catalyst for the desiredchemical conversion process, e.g., hydrodewaxing, ethylbenzeneconversion, etc. For instance, a mild treatment under the second step ofthe present method will produce a final activity-modified zeolite, e.g,ZSM-5, with changed X-ray diffraction pattern. The change will be somereduced intensity and broader lines indicating structural modification.Zeolite ZSM-5 subjected to mild second step hydrogen fluoride treatment,on aging, the orthorhombic structure transforms to the tetragonal formproviding a highly active and stable catalyst.

The third step of the method involves calcining the product zeolite ofthe second step. This will be accomplished by heating the same at atemperature within the range of from about 200° C. to 600° C. in aninert atmosphere of air, nitrogen, etc. at atmospheric, superatmosphericor subatmospheric pressure for between 10 minutes and 48 hours.

The fourth step of the method involves contacting the calcined productzeolite of the third step with an ammonium exchange solution. Theammonium exchange solution contacting step may be conducted for a periodof time of from about 1 hour to about 20 hours at a temperature of fromambient to about 100° C. The actual ammoniumm exchange material whichmay be used is not narrowly critical and will normally be an inorganicsalt, such as ammonium nitrate, ammonium sulfate, ammonium chloride,etc., or ammonium hydroxide. The solution will normally be aqueous atfrom about 0.1 to about 5 Normal, preferably about 1 Normal.

The fifth step of the method of the present invention involves calciningthe ammonium exchanged zeolite from the fourth step by heating the sameat a temperature within the range of from about 200° C. to about 600° C.in an inert atmosphere at atmospheric, subatmospheric orsuperatmospheric pressure for between 10 minutes and 48 hours.

Synthetic zeolites to be tailored by the present method may becharacterized as having a crystal structure which provides constrainedaccess to and egress from the intracrystalline free space by virtue ofhaving a pore dimension greater than about 5 Angstroms and pore windowsof about a size such as would be provided by 10-membered rings of oxygenatoms. It is to be understood, of course, that these rings are thoseformed by the regular disposition of the tetrahedra making up theanionic framework of the crystalline zeolite, the oxygen atomsthemselves being bonded to the silicon or aluminum atoms at the centersof the tetrahedra. Briefly, the preferred zeolites useful in thisinvention possess, in combination, a silica to alumina ratio of at leastabout 12, and a structure providing constrained access to thecrystalline free space.

The silica to alumina ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in any binder or in cationic or otherform within the channels. Although zeolites with a silica to aluminaratio of at least 12 are useful, it is preferred to use such zeoliteshaving higher ratios of at least about 30. Such zeolites, afteractivation, acquire an intracrystalline sorption capacity for normalhexane which is greater than that for water, i.e. they exhibit"hydrophobic" properties. It is believed that this hydrophobic characteris advantageous in the chemical conversions to be conducted with thefinal product zeolites.

Synthetic crystalline zeolites usefully tailored by this inventionfreely sorb normal hexane and have a pore dimension greater than about 5Angstroms. In addition, the structure must provide constrained access tolarger molecules. It is sometimes possible to judge from a known crystalstructure whether such constrained access exists. For example, if theonly pore windows in a crystal are formed by 8-membered rings of oxygenatoms, then access by molecules of larger cross-section than normalhexane is excluded and the zeolite is not of the desired type. Windowsof 10-membered rings are preferred, although, in some instances,excessive puckering or pore blockage may render these catalystsineffective. Twelve-membered rings do not generally appear to offersufficient constraint to produce the advantageous conversions, althoughpuckered structures exist such as TMA offretitte which is a knowneffective zeolite. Also, structures can be conceived, due to poreblockage or other cause, that may be operative.

Rather than attempt to judge from crystal structure whether or not aparticular zeolite possesses the necessary constrained access, a simpledetermination of the "constraint index" may be made by passingcontinuously a mixture of an equal weight of normal hexane and3-methylpentane over a small sample, approximately 1 gram or less, ofzeolite at atmospheric pressure according to the following procedure. Asample of the zeolite, in the form of pellets or extrudate, is crushedto a particle size about that of coarse sand and placed in a glass tube.Prior to testing, the zeolite is treated with a stream of air at about538° C. for at least 15 minutes. The zeolite is then flushed with heliumand the temperature adjusted between about 288° C. and 510° C. to givean overall conversion between 10% and 60%. The mixture of hydrocarbonsis passed at 1 liquid hourly space velocity (i.e., 1 volume of liquidhydrocarbon per volume of zeolite per hour) over the zeolite with ahelium dilution to give a helium to total hydrocarbon mole ratio of 4:1.After 20 minutes on stream, a sample of the effluent is taken andanalyzed, most conveniently by gas chromatography, to determine thefraction remaining unchanged for each of the two hydrocarbons.

The "Constraint Index" is calculated as follows: ##EQU1##

The Constraint Index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Zeolites suitable for the presentinvention are those having a Constraint Index of 1 to 12. ConstraintIndex (CI) values for some typical zeolites are:

    ______________________________________                                        Zeolite             CI                                                        ______________________________________                                        ZSM-4               0.5                                                       ZSM-5               8.3                                                       ZSM-11              8.7                                                       ZSM-12              2                                                         ZSM-23              9.1                                                       ZSM-35              4.5                                                       ZSM-38              2                                                         ZSM-48              3.4                                                       TMA Offretite       3.7                                                       Beta                0.6                                                       H--Zeolon (mordenite)                                                                             0.4                                                       REY                 0.4                                                       Amorphous Silica-Alumina                                                                          0.6                                                       Erionite            38                                                        ______________________________________                                    

In a preferred aspect of this invention, the zeolites modified herebyare selected as those providing among other things a crystal frameworkdensity, in the dry hydrogen form, of not less than about 1.6 gram percubic centimeter. It has been found that zeolites which satisfy allthree of the discussed criteria are most desired for several reasons.When hydrocarbon products or by-products are catalytically formed, forexample, such zeolites tend to maximize the production of gasolineboiling range hydrocarbon products. Therefore, the preferred zeolitesuseful with respect to this invention are those having a ConstraintIndex as defined above of about 1 to about 12, a silica to alumina moleratio of at least about 12 and a dried crystal density of not less thanabout 1.6 grams per cubic centimeter. The dry density for knownstructures may be calculated from the number of silicon plus aluminumatoms per 1000 cubic Angstroms, as given, e.g., on Page 19 of thearticle ZEOLITE STRUCTURE by W. M. Meier. This paper, the entirecontents of which are incorporated herein by reference, is included inPROCEEDINGS OF THE CONFERENCE ON MOLECULAR SIEVES, (London, April 1967)published by the Society of Chemical Industry, London, 1968.

When the crystal structure is unknown, the crystal framework density maybe determined by classical pycnometer techniques. For example, it may bedetermined by immersing the dry hydrogen form of the zeolite in anorganic solvent which is not sorbed by the crystal. Or, the crystaldensity may be determined by mercury porosimetry, since mercury willfill the interstices between crystals but will not penetrate theintracrystalline free space.

It is possible that the unusual sustained activity and stability of thisspecial class of zeolites is associated with its high crystal anionicframework density of not less than about 1.6 grams per cubic centimeter.This high density must necessarily be associated with a relatively smallamount of free space within the crystal, which might be expected toresult in more stable structures. This free space, however, is importantas the locus of catalytic activity.

Crystal framework densities of some typical zeolites, including somewhich are not within the purview of this invention, are:

    ______________________________________                                                   Void         Framework                                                        Volume       Density                                               ______________________________________                                        Ferrierite   0.28     cc/cc     1.76 g/cc                                     Mordenite    .28                1.7                                           ZSM-5, -11   .29                1.79                                          ZSM-12       --                 1.8                                           ZSM-23       --                 2.0                                           Dachiardite  .32                1.72                                          L            .32                1.61                                          Clinoptilolite                                                                             .34                1.71                                          Laumontite   .34                1.77                                          ZSM-4 (Omega)                                                                              .38                1.65                                          Heulandite   .39                1.69                                          P            .41                1.57                                          Offretite    .40                1.55                                          Levynite     .40                1.54                                          Erionite     .35                1.51                                          Gmelinite    .44                1.46                                          Chabazite    .47                1.45                                          A            .5                 1.3                                           Y            .48                1.27                                          ______________________________________                                    

In practicing a particularly desired chemical conversion process, it maybe useful to incorporate the crystalline zeolite modified in accordanceherewith with a matrix comprising another material resistant to thetemperature and other conditions employed in the process. Such matrixmaterial is useful as a binder and imparts greater resistance to thecatalyst for the severe temperature, pressure and reactant feed streamvelocity conditions encountered in, for example, many crackingprocesses.

Useful matrix materials include both synthetic and naturally occurringsubstances, as well as inorganic materials such as clay, silica and/ormetal oxides. The latter may be either naturally occurring or in theform of gelatinous precipitates or gels including mixtures of silica andmetal oxides. Naturally occurring clays which can be composited with thezeolite include those of the montmorillonite and kaolin families, whichfamilies include the sub-bentonites and the kaolins commonly known asDixie, McNamee, Georgia and Florida clays or others in which the mainmineral constituent is halloysite, kaolinite, dickite, nacrite oranauxite. Such clays can be used in the raw states as originally minedor initially subjected to calcination, acid treatment or chemicalmodification.

In addition to the foregoing materials, the zeolites modified hereby maybe composited with a porous matrix material, such as alumina,silica-alumina, silica-magnesium, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The matrix may bein the form of a cogel. The relative proportions of zeolite componentand inorganic oxide gel matrix, on an anhydrous basis, may vary widelywith the modified zeolite content ranging from about 1 to about 99percent by weight and more usually from about 5 to about 80 percent byweight of the dry composite.

The activity altered zeolites prepared by the present method are usefulas catalyst components for various organic compound, e.g., hydrocarboncompound, conversion reactions. Such reactions include, as non-limitingexamples, toluene disproportionation, wherein the reaction conditionsinclude a temperature of from about 450° C. to about 540° C., a pressureof from about 400 psig to about 600 psig and a weight hourly spacevelocity of from about 2 to about 4; and lube oil dewaxing, wherein thereaction conditions include a temperature of from about 285° C. to about370° C., a pressure of from about 300 psig to about 500 psig and aweight hourly space velocity of from about 0.5 to about 1; and vaporphase xylenes isomerization at a temperature in the range of from about230° C. to about 485° C., a pressure in the range of from about 50 psigto about 500 psig, a weight hourly space velocity of from about 0.1 toabout 200 and a hydrogen/hydrocarbon mole ratio of from about 0 to about100. In general, therefore, such organic compound conversion reactionsmay be said to require a temperature of from about 230° C. to about 540°C., a pressure of from about 50 psig to about 600 psig, a weight hourlyspace velocity of from about 0.1 to about 200 and a hydrogen/hydrocarbonmole ratio of from about 0 to about 100.

The following examples will illustrate the novel method of the presentinvention.

EXAMPLE 1

A quantity of zeolite ZSM-5 was synthesized by the method taught in U.S.Pat. No. 3,702,886 with tripropylamine as the bulky cation source.

EXAMPLE 2

A sample of the as synthesized zeolite ZSM-5 from Example 1 was calcinedat 500° C. for 4 hours and then subjected to the Alpha Test. It wasfound to have an Alpha Value of 242.

EXAMPLE 3

Desiring to tailor a zeolite to have an Alpha activity of closer to 150,a 2 gram sample of the as synthesized, uncalcined zeolite ZSM-5 fromExample 1 was mixed with a 0.1 N aqueous solution of hydrogen fluoride(1 grams HF and 500 grams H₂ O). The mixture was slurried for 3 hours atroom temperature (24° C.) and atmospheric pressure. The mixture wasfilter separated and the hydrogen fluoride solution replaced for furtherslurrying for 3 hours at room temperature and atmospheric pressure. Themixture was again filter separated and the zeolite washed with water atroom temperature and dried at 130° C. The hydrogen fluoride contactedzeolite was then calcined at 500° C. for 4 hours. The calcined zeolitewas then treated by contact with 300 cc of 1 N NH₄ Cl solution at 100°C. for 4 hours, water washed, filtered and dried at 130° C. The zeolitewas then calcined for 4 hours at 500° C. in a muffle furnace. The AlphaValue of this treated zeolite was 155.

As is known in the art, the Alpha Value is an approximate indication ofthe catalytic cracking activity of the catalyst compared to a standardcatalyst and it gives the relative rate constant (rate of normal hexaneconversion per volume of catalyst per unit time). It is based on theactivity of the highly active silica-alumina cracking catalyst taken asan Alpha of 1 (rate constant=0.016). The Alpha Test is described in U.S.Pat. No. 3,354,078 and in The Journal of Catalysis, Vol. IV, pp. 522-529(August 1965).

What is claimed is:
 1. A method for altering catalytic activity of asynthetic crystalline zeolite characterized as having a crystalstructure which provides constrained access to and egress from theintracrystalline free space by virtue of having a pore dimension greaterthan about 5 Angstroms and pore windows of about a size as would beprovided by 10-membered rings of oxygen atoms which comprises thesequential steps of synthesizing said zeolite from a reaction mixturecontaining a source of bulky organic cations, contacting the synthesizedzeolite with an aqueous hydrogen fluoride solution of from about 0.005Normal to about 0.5 Normal at a temperature of from about ambient toabout 100° C. and a pressure of from about atmospheric to about 40 psigfor a contact time of from about 1 hour to about 10 hours, calcining thehydrogen fluoride solution contacted zeolite at a temperature of fromabout 200° C. to about 600° C., contacting the calcined zeolite with anammonium exchange solution at a temperature of from about ambient toabout 100° C., and calcining the ammonium exchange solution contactedzeolite at a temperature of from about 200° C. to about 600° C.
 2. Themethod of claim 1 wherein said crystalline zeolite is characterized by asilica/aluminum mole ratio of at least
 12. 3. The method of claim 2wherein said crystalline zeolite is selected from the group consistingof ZSM-5, ZSM-11, ZSM-12, ZSM-23 ZSM-35, ZSM-38 and ZSM-48.
 4. Themethod of claim 3 wherein said crystalline zeolite is ZSM-5.
 5. Themethod of claim 1 wherein said source of bulky organic cations isselected from the group consisting of trialkylamines, wherein alkyl isfrom 1 to 20 carbon atoms, onium compounds and compounds containingmultiple cationic centers.
 6. The method of claim 5 wherein said sourceof bulky organic cations is onium compounds having the formula

    R.sub.4 M.sup.+ X.sup.-

wherein R is alkyl of from 1 to 20 carbon atoms, heteroalkyl of from 1to 20 carbon atoms, aryl, heteroaryl, cycloalkyl of from 3 to 6 carbonatoms, cycloheteroalkyl of from 3 to 6 carbon atoms, or combinationsthereof; M is a quadricoordinate element or a heteroatom in analicyclic, heteroalicyclic or heteroaromatic structure; and X is ananion.
 7. The method of claim 5 wherein said source of bulky organiccations is compounds containing multiple cationic centers having theformula

    ((R).sub.3 M.sup.+ (Z).sub.n M.sup.+ (R).sub.3)(X.sup.-).sub.2

wherein R is alkyl of from 1 to 20 carbon atoms, heteroalkyl of from 1to 20 carbon atoms, aryl, heteroaryl, cycloalkyl of from 3 to 6 carbonatoms, cycloheteroalkyl of from 3 to 6 carbon atoms, or combinationsthereof; M is a quadricoordinate element or a heteroatom in analicyclic, heteroalicyclic or heteroaromatic structure; X is an anion; Zis a bridging member selected from the group consisting of alkyl of from1 to 20 carbon atoms, alkenyl of from 2 to 20 carbon atoms, aryl,heteroalkyl of from 1 to 20 carbon atoms, heteroalkenyl of from 2 to 20carbon atoms and heteroaryl; and n is a number of from 1 to about
 50. 8.The method of claim 5 wherein said source of bulky organic cations is atrialkylamine wherein alkyl is from 1 to 20 carbon atoms.
 9. The methodof claim 1 wherein said ammonium exchange solution is an aqueoussolution of an ammonium salt or ammonium hydroxide.
 10. The method ofclaim 9 wherein said ammonium salt is ammonium nitrate, ammonium sulfateor ammonium chloride.
 11. A method for altering catalytic activity of asynthetic crystalline zeolite having a constraint index of from about 1to about 12 and a silica/alumina mole ratio of at least 12 whichcomprises the sequential steps of synthesizing said zeolite from areaction mixture containing a source of bulky organic cations,contacting the synthesized zeolite with an aqueous hydrogen fluoridesolution of from about 0.005 Normal to about 0.5 Normal at a temperatureof from about ambient to about 100° C. and a pressure of from aboutatmospheric to about 40 psig for a contact time of from about 1 hour toabout 10 hours, calcining the hydrogen fluoride solution contactedzeolite at a temperature of from about 200° C. to about 600° C.,contacting the calcined zeolite with an ammonium exchange solution at atemperature of from about ambient to about 100° C., and calcining theammonium exchange solution contacted zeolite at a temperature of fromabout 200° C. to about 600° C.
 12. The method of claim 11 wherein saidsource of bulky organic cations is selected from the group consisting oftrialkylamines, wherein alkyl is from 1 to 20 carbon atoms, oniumcompounds and compounds containing multiple cationic centers.
 13. Themethod of claim 12 wherein said source of bulky organic cations is oniumcompounds having the formula

    R.sub.4 M.sup.+ X.sup.-

wherein R is alkyl of from 1 to 20 carbon atoms, heteroalkyl of from 1to 20 carbon atoms, aryl, heteroaryl, cycloalkyl of from 3 to 6 carbonatoms, cycloheteroalkyl of from 3 to 6 carbon atoms, or combinationsthereof; M is a quadricoordinate element or a heteroatom in analicyclic, heteroalicyclic or heteroaromatic structure; and X is ananion.
 14. The method of claim 12 wherein said source of bulky organiccations is compounds containing multiple centers having the formula

    ((R).sub.3 M.sup.+ (Z).sub.n M.sup.+ (R).sub.3)(X.sup.-).sub.2

wherein R is alkyl of from 1 to 20 carbon atoms, heteroalkyl of from 1to 20 carbon atoms, aryl, heteroaryl, cycloalkyl of from 3 to 6 carbonatoms, cycloheteroalkyl of from 3 to 6 carbon atoms, or combinationsthereof; M is a quadricoordinate element or a heteroatom in analicyclic, heteroalicyclic or heteroaromatic structure; X is an anion; Zis a bridging member selected from the group consisting of alkyl of from1 to 20 carbon atoms, alkenyl of from 2 to 20 carbon atoms, aryl,heteroalkyl of from 1 to 20 carbon atoms, heteroalkenyl of from 2 to 20carbon atoms and heteroaryl; and n is a number of from 1 to about 50.15. The method of claim 12 wherein said source of bulky organic cationsis a trialkylamine wherein alkyl is from 1 to 20 carbon atoms.
 16. Amethod for altering catalytic activity of a synthetic crystallinezeolite having the structure of zeolite ZSM-5 which comprises thesequential steps of synthesizing said zeolite from a reaction mixturecontaining a source of bulky organic cations, contacting the synthesizedzeolite with an aqueous hydrogen fluoride solution of from about 0.005Normal to about 0.5 Normal at a temperature of from about ambient toabout 100° C. and a pressure of from about atmospheric to about 40 psigfor a contact time of from about 1 hour to about 10 hours, calcining thehydrogen fluoride solution contacted zeolite at a temperature of fromabout 200° C. to about 600° C., contacting the calcined zeolite with anammonium exchange solution at a temperature of from about ambient toabout 100° C., and calcining the ammonium exchange solution contactedzeolite at a temperature of from about 200° C. to about 600° C.